Description: Thallus crustose-subsquamulose, episubstratic, consisting of scattered to clustered, reddish brown, 0.3-1.8 mm wide, angular areoles, or reduced to the thalline margin of the apothecia. Algal layer even, continuous. Apothecia lecanorine, 0.2-1 mm across, mostly one per areole and occupying most of its surface, with a smooth, sometimes umbonate, brown-black disc, and a thick, raised, smooth thalline margin. Epithecium brownish; hymenium colourless, 70-120 µm high; paraphyses 1.5-2 µm thick at base, the apical cells 2-3 µm wide; hypothecium colourless. Asci c. 200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid to subcylindrical, 4-6.5 x 1-2.5 µm. Photobiont chlorococoid. Spot test: upper cortex K+ yellow then red (needle-like crystals), C-, KC-, P- or P+ yellowish. Chemistry: norstictic acid.
Note: on hard siliceous rocks, especially granite, near the coast. A Mediterranean-Atlantic European species, reported from a few localities, from the British Isles to Portugal, and also known from the Aegean Islands.